1. Field of the Invention
This invention relates to a technique suitable to be applied to a position detection apparatus and a sensor unit, and more particularly to a technique for enhancing the position detection performance of an electromagnetic induction type digitizer.
2. Description of the Related Art
Various apparatus are available as an inputting apparatus for applying position information to a computer. One of such apparatus is a position detection apparatus generally called a digitizer.
The position detection apparatus is an inputting apparatus having a detection plane for detecting two-dimensional position information, on which a position pointer in the form of a pen is operated, in such a manner as to carry out drawing. The position detection apparatus has been widely popularized as an inputting apparatus suitable for the user who uses an application program in which drawing must be carried out quickly and accurately in the fields of design, art and so forth. The position detection apparatus is configured from a position pointer in the form of a pen for pointing to a position and a sensor unit for detecting a point pointed to by the position pointer and converting the detected information into two-dimensional position information which can be utilized by a computer and then outputting the resulting information.
The sensor unit includes a position detection plane for detecting the position of the position pointer. A printed board wherein loop coils extending in an X-axis direction and a Y-axis direction is embedded in the position detection plane.
The loop coils are each supplied with current having a specific frequency so that a magnetic field is generated therefrom. As a result, a resonance circuit included in the position pointer resonates when the position pointer is positioned in the proximity of a loop coil which is generating the magnetic field. Then, an induced magnetic field generated from the resonance circuit of the position pointer is received by a loop coil. The position of the position pointer is detected by carrying out the operation described above for each of the loop coils.
Japanese Patent Laid-Open No. 2007-166147 assigned to the assignee of the present patent application is listed as a prior art document.